The present invention relates to a high pressure-low pressure steam turbine and more specifically to a method of forming a turbine rotor of a high temperature compatible steel alloy and a low temperature compatible steel alloy by welding together of rotor segments composed of differing steel alloy.
Usually, turbine rotor alloys are designed for either optimum high temperature or optimum low temperature properties. The high temperature alloy has very poor low temperature properties while the low temperature alloy has very poor high temperature properties.
In the formation of a 100 to 200 Mw turbine, the rotor material becomes a major concern. The high-pressure end of the rotor must have adequate creep and fatigue properties at temperatures in the range of 1000.degree. F. (538.degree. C.), whereas the low-pressure end of the rotor must have a 100 ksi minimum yield strength, stress corrosion resistance, fatigue strength and fracture toughness. High temperature, pressure, rotor alloys, usually low alloy steel containing chromium, molybdenum and vanadium (CrMoV), have excellent creep properties but extremely poor fracture toughness, about 75.degree. F. (24.degree. C.). The low temperature, pressure, rotor alloys, usually low alloy steel containing nickel, chromium, molybdenum and vanadium (NiCrMoV), have poor creep properties above about 800.degree. F., (427.degree. C.).
It is an object of the present invention to provide a method of forming a turbine rotor for use in a high pressure-low pressure steam turbine that will have desirable properties in both the high temperature and low temperature regions of the turbine.